Introduction

The functions provided by this extension check whether a character
or string falls into a certain character class according to the
current locale (see also setlocale()).

When called with an integer argument these functions
behave exactly like their C counterparts from
ctype.h.
It means that if you pass an integer smaller than 256 it will use the
ASCII value of it to see if it fits in the specified range (digits are in
0x30-0x39). If the number is between -128 and -1 inclusive then 256 will
be added and the check will be done on that.

When called with a string argument they will check
every character in the string and will only return
TRUE if every character in the string matches the
requested criteria. When called with an empty string
the result will always be TRUE in PHP < 5.1 and FALSE since 5.1.

Passing anything else but a string or integer will
return FALSE immediately.

It should be noted that ctype functions are always preferred over
regular expressions, and even to some equivalent "str_*" and "is_*" functions.
This is because of the fact that ctype uses a native C library and thus
processes significantly faster.

Note:

These functions are not related to the Python "ctypes" library at all.
The extension name stems from the ctype.h C header
file that their C equivalents are defined in.

This extension also predates Python "ctypes" so any confusion
caused by this naming is hardly our fault ...